I've had the same trouble, been looking to get mine done too, but thought I'd try and get one from a breakers as I thought the RS4 and normal A4 were the same. I know the S4 has a ridiculous bulge in it and just looks stupid, so i've been hunting through breakers yards for a couple of months. When I asked on here previously nobody seemed to know the part number!
Problem I had was most breakers will not just sell you the bottom strip, they want to flog the whole door! I understand that approach, but then I stumbled across one which strips them off and sells them indiviually. Result! Or so I thought. lol.
It turns out the one I ordered had a slightly different profile, it's not a massive difference, but probably has a 5mm bulge on it compared to the flat RS4 ones. Luckily the breaker had the trims for the rest of the doors off the same car, so I bought all four to make sure they match. Was £90 for all 4 including delivery which I thought was decent as I was being quoted that much for a single door. They've turned up today so will try and get some pictures up later.
FYI - the breaker I used was these guys.
https://store.prestigemotorservices.co. ... 26110.html